Protection by alpha2-macroglobulin of tissue plasminogen activator against inhibition by plasminogen activator inhibitor-1

Bacterial staphylokinase as a promising third-generation drug in the treatment for vascular occlusion

Vascular occlusion is one of the major causes of mortality and morbidity. Blood vessel blockage can lead to thrombotic complications such as myocardial infarction, stroke, deep venous thrombosis, peripheral occlusive disease, and pulmonary embolism. Thrombolytic therapy currently aims to rectify this through the administration of recombinant tissue plasminogen activator. Research is underway to design an ideal thrombolytic drug with the lowest risk. Despite the potent clot lysis achievable using approved thrombolytic drugs such as alteplase, reteplase, streptokinase, tenecteplase, and some other fibrinolytic agents, there are some drawbacks, such as high production cost, systemic bleeding, intracranial hemorrhage, vessel re-occlusion by platelet-rich and retracted secondary clots, and non-fibrin specificity. In comparison, bacterial staphylokinase, is a new, small-size plasminogen activator, unlike bacterial streptokinase, it hinders the systemic degradation of fibrinogen and reduces the risk of severe hemorrhage. A fibrin-bound plasmin-staphylokinase complex shows high resistance to a₂-antiplasmin-related inhibition. Staphylokinase has the potential to be considered as a promising thrombolytic agent with properties of cost-effective production and the least side effects.

Functional proteomics of kallikrein-related peptidases in ovarian cancer ascites fluid

Kallikrein-related peptidases (KLKs) are secreted serine proteinases with trypsin or chymotrypsin-like activity. Several family members, such as KLKs 6 and 10, are potential ovarian cancer biomarkers. Recently, using a newly developed assay for active KLK6, we found that only a very small proportion of immunoreactive KLK6 in tumor-derived clinical samples (malignant ascites fluid), in cerebrospinal fluid, and in cancer cell line supernatants is enzymatically active. We therefore hypothesized that a proportion of other immunoreactive KLKs in such samples could be present, but might be partly complexed to endogenous serine proteinase inhibitors. Using a combination of immunological isolation of the enzymes, activity-based probe analysis and proteomics, we identified active KLK10 in ovarian cancer ascites and we provide preliminary data that the activity of other KLKs present in these samples can be decreased by known proteinase inhibitors (e.g., alpha2-macroglobulin, alpha1-antitrypsin). Our data suggest that the enzymatic activity of ovarian cancer-released KLKs that are detected by regular immunoassays is low in vivo and very likely regulated by proteinase inhibitors.

Effects of alpha(2)-macroglobulin and antithrombin on thrombin generation and inhibition in cord and adult plasma

Thromboembolic complications rarely occur during infancy and childhood. It has been reported that increased capacity of cord plasma to inhibit thrombin due to elevated alpha(2)-macroglobulin (alpha(2)-M) levels may in part provide protection from thrombosis. In antithrombin (AT)-deficient plasma, alpha(2)-M exhibits anticoagulant action by complexing substantial amounts of generated free thrombin. It has been suggested that alpha(2)-M has the same impact on thrombin inhibition as AT, the most important thrombin inhibitor in adult plasma. The aim of our study was to examine this assumption by determining time-courses of free thrombin generation and prothrombin activation. Additionally, the amount of thrombin complexed to alpha(2)-M was assessed by comparing the heights of the end-level of amidolytic activity curves (AACs) after extrinsic activation of platelet poor plasma in the presence of different concentrations of AT or alpha(2)-M. Increasing the AT content by 30% resulted in significantly suppressed generation of free thrombin and prothrombin fragment 1+2 (F1+2) in cord and adult plasma. In contrast, increasing the alpha(2)-M content in plasma containing physiologic amounts of AT by the same percentage had no effect on free thrombin generation and on F1+2 generation in both cord and adult plasma. In addition, the effect of AT supplementation on the end-level of the AACs was significantly higher compared to the effect of alpha(2)-M supplementation. Since alpha(2)-M, in contrast to AT, had no effect on free thrombin generation and prothrombin activation, our study suggests that the action between alpha(2)-M and thrombin might not be fast enough to prevent thrombin from its feedback activation in both cord and adult plasma and, therefore, in cord and adult plasma containing physiological amounts of AT alterations of the alpha(2)-M content had no effect on thrombin generation and inhibition.

The hepatic clearance of recombinant tissue-type plasminogen activator decreases after an inflammatory stimulus

We have shown that tissue-type plasminogen activator (tPA) and plasma kallikrein share a common pathway for liver clearance and that the hepatic clearance rate of plasma kallikrein increases during the acute-phase (AP) response. We now report the clearance of tPA from the circulation and by the isolated, exsanguinated and in situ perfused rat liver during the AP response (48-h ex-turpentine treatment). For the sake of comparison, the hepatic clearance of a tissue kallikrein and thrombin was also studied. We verified that, in vivo, the clearance of 125I-tPA from the circulation of turpentine-treated rats (2.2 +/- 0.2 ml/min, N = 7) decreases significantly (P = 0.016) when compared to normal rats (3.2 +/- 0.3 ml/min, N = 6). The AP response does not modify the tissue distribution of administered 125I-tPA and the liver accounts for most of the 125I-tPA (>80%) cleared from the circulation. The clearance rate of tPA by the isolated and perfused liver of turpentine-treated rats (15.5 +/- 1.3 microg/min, N = 4) was slower (P = 0.003) than the clearance rate by the liver of normal rats (22. 5 +/- 0.7 microg/min, N = 10). After the inflammatory stimulus and additional Kupffer cell ablation (GdCl3 treatment), tPA was cleared by the perfused liver at 16.2 +/- 2.4 microg/min (N = 5), suggesting that Kupffer cells have a minor influence on the hepatic tPA clearance during the AP response. In contrast, hepatic clearance rates of thrombin and pancreatic kallikrein were not altered during the AP response. These results contribute to explaining why the thrombolytic efficacy of tPA does not correlate with the dose administered.